What If You Could Become Invisible to Mosquitoes?
Many experiments on mosquito vision take place in wind tunnels, large chambers that can cost tens of thousands of dollars. In prior experiments, mosquitoes placed in the wind tunnel and given a whiff of carbon dioxide chose to fly to a dark spot over a white one.
Dr. Montell’s lab does not have a wind tunnel, so Dr. Zhan designed an inexpensive setup — a cage with a black circle and a white circle inside — that cost less than $100 and delivered the same results as a wind tunnel. In the spring of 2019, Dr. Zhan conducted spot tests in the cage. In the fall, Jeff Riffell, a biologist at the University of Washington, along with Claire Rusch, a graduate student, and Diego Alonso San Alberto, a postdoctoral fellow, ran the same experiments using a wind tunnel to double-check the original results.
Dr. Montell and Dr. Zhan suspected that one of the five light-sensing proteins expressed in the mosquito’s eye might be the key to eliminating its ability to visually seek out human hosts by sensing dark colors. First, they decided to knock out the rhodopsin protein Op1. Op1, the most widely expressed vision protein in the mosquito’s compound eyes, seemed the best candidate for interfering with the mosquito’s vision. Dr. Zhan injected the mutation into thousands of tiny mosquito eggs using a tool with a special needle with a very tiny tip.
After his wee mutants had grown into adults, Dr. Zhan sucked 10 or so females into a tube using a mouth-controlled aspirator. With each group, he held his breath, walked over to the cage and released the females with one big exhale.
The Op1 mutants behaved exactly like the wild-type Aedes aegypti: After huffing carbon dioxide, they flew directly to the black dot in the cage. Dr. Montell and Dr. Zhan tried again, this time knocking out Op2, a closely related rhodopsin. Still, the Op2 mutants showed no meaningful decline in their vision.
But when the researchers knocked out both proteins, the mosquitoes whizzed around aimlessly, showing no preference between the white circle and black circles. They had lost their ability to seek dark-colored hosts.
Were the mosquitoes blind altogether, or just blind to people? To answer this question, Dr. Montell and Dr. Zhan ran a series of tests to see how the double mutants responded to light.